Flathead Grey Mullet Mugil Cephalus Research Articles

Flathead grey mullet (Mugil cephalus) juveniles exhibit consistent proactive and reactive stress coping styles

Stress coping styles (SCS) are defined as a coherent set of individual physiological and behavioural differences in stress responses that are consistent across context and over time. Nowadays, an increased attention has been paid to fish welfare in aquaculture production and to consistent behavioural response to stress in captivity, since these aspects present direct implications on fish health, quality and farming productivity. Therefore, the present study aimed to evaluate the differences between proactive and reactive stress coping styles and their consistency over time and across contexts in flathead grey mullet Mugil cephalus juveniles reared in captivity. Fish were submitted to two runs of a set of behavioural tests, with a four-months interval: one group test (risk-taking test) and three individual tests (restraining, predator and confinement tests), followed by the quantification of blood cortisol and glucose concentrations (control and post-stress). Results confirmed the existence of proactive and reactive SCS in mullet juveniles and demostrated that behavioural responses in most of the tests were consistent over time (between runs) and across contexts (among tests). Fish that crossed from the safe to the risky area in the risk-taking test also displayed higher activity and escape attempts and lower basal levels of cortisol and glucose than fish than did not cross. This work reported for the first time the consistency of stress coping styles over time and across contexts in M. cephalus juveniles. Due to the increased interest in understanding adaptive mechanisms underlying consistent individual behaviours in response to stressful situations, are of interest for the aquaculture industry to improve productive performance of this fish species. Further studies are required to investigate how different selective pressures might influence the expression and consistency of SCS over time and across contexts.

Simulated transport of flathead grey mullet Mugil cephalus eggs: Effects of density and duration

Flathead grey mullet has a great potential as a low trophic level aquaculture species, however captive rearing is still hampered by the lack of well-established production protocols. Here we examined the effects of transport time and egg loading density on water quality, egg survival, hatching success and early larvae performance when shipped for 8, 16 and 24 h at 500 and 1500 eggs L−1. When no water conditioners were used, survival immediately after transport was consistently over 60% up to 16 h shipment for both densities tested, with minimum values of 40% for 1500 eggs L−1. Density and transport time did not influence hatching rate (p > .05) which ranged between 31 and 54% after 8 and 16 hour transport. However, manipulation after 8 and 24 h transport led to a significant drop in early larvae survival regardless the density tested (20% and 5% respectively) compared to 16 h transport (40%) (p < .05). Hence, the results indicate that grey mullet is sensitive when manipulated as early hatched larvae and when eggs undergo blastophore closure at circa 20 h post-fertilization.The tested egg stocking densities do not deteriorate water quality to lethal levels in terms of pH, NO2 and NO3 especially for short and medium transportation times, however, 24 h transportation induces an accumulation of ammonia affecting the long-term survival of larvae. When basic technology is available (i.e. no water conditioners, refrigerated vehicles), we suggest manipulating grey mullet eggs at 28 h post fertilization for best results in terms of hatching rate and early larvae survival.

Description of the Sex Hormone-Secreting Cells during Oocyte Development and Atresia in Flathead Grey Mullet Mugil cephalus (Mugilidae) in Al-Bardawil Lagoon, Egypt

The present study described the changes of steroidogenic cells accompanied the ovarian maturation in flathead grey mullet, Mugil cephalus, from Al-Bardawil lagoon. Here, five periods of ovarian development including previtellogenesis, vitellogenesis (early, mid, and late), and pre-spawning ones were successfully obtained from mullet female inhabiting Al-Bardawill lagoon. In addition, abnormal feature of atresia was noticed in the vitellogenic stages of the ovaries. In atretic follicles, the granulosa cells converted into active phagocytic cells digesting and consuming the yolk in those oocytes. The histochemical and ultrastructural observations showed that the follicular cells, theca and granulosa of the developing oocytes are the site of the sex hormones synthesis. Both theca and granulosa have manifested both quantitative and qualitative alterations concomitant during oogenesis as reflected by an obvious increase in number, size, and content of lipid droplets of those cells. In conclusion, the present observations show the histological and ultrastructural changes of steroidogenic cells during ovarian maturation and atresia of the grey mullet. This new information is essential for managing and preserving Al-Bardawil lagoon as a natural source of mullet broodstock and for achieving sustainable development for this fish.

Description of the Sex Hormone-Secreting Cells during Oocyte Development and Atresia in Flathead Grey Mullet Mugil cephalus (Mugilidae) in Al-Bardawil Lagoon, Egypt

Description of the Sex Hormone-Secreting Cells during Oocyte Development and Atresia in Flathead Grey Mullet Mugil cephalus (Mugilidae) in Al-Bardawil Lagoon, Egypt

Myxozoan infection in thinlip mullet Chelon ramada (Mugiliformes: Mugilidae) in the Sea of Galilee

Mullets (Mugilidae) are economically important fish in Israel. Two species of mugilids (i.e., the thinlip mullet Chelon ramada and the flathead grey mullet Mugil cephalus) have been stocked in the Sea of Galilee (Lake Kinneret) in order to increase fishermen’s income and lake water quality. These catadromous species do not reproduce in the lake, consequently, fingerlings have been introduced every year since 1958. Few additional mugilid species have been introduced unintentionally together with these two species, including C. labrosus. Following a survey of myxozoan infections in the Sea of Galilee, we described Myxobolus pupkoi n. sp. infecting the gill arches of C. labrosus, and reported Myxobolus exiguus from visceral peritoneum and gall bladder of C. ramada. Our study indicates that the parasites infecting C. ramada and C. labrosus belong to a lineage of myxozoans infecting mugilids. This result suggests that the infection took place in the Mediterranean Sea, where the fingerlings were caught, before their introduction into the Sea of Galilee. Since 2018 only farm-raised fingerlings have been introduced. We thus recommend to closely monitor the presence of these parasites in the future to determine if the presence of parasites disappear with the introduction of farm-raised fingerlings.

First description of Vibrio harveyi as the causative agent of morbidity and mortality in farmed flathead grey mullet Mugil cephalus

Flathead grey mullet Mugil cephalus is an important species in the aquaculture industry in the Mediterranean basin and throughout the world. During the last 10 yr, M. cephalus breeding stocks, larvae, and juveniles cultured in Eilat (Israel) have shown neurological signs such as uncoordinated circular swimming, while also presenting oral hemorrhages. Death follows days after the onset of the clinical signs, and mortality rates may reach 80% in some cases, causing high economical losses. Bacteriology isolations from different organs, including the brain, and a Koch’s postulate experiment, confirmed Vibrio harveyi as the causative agent. Histological analyses showed the presence of the bacterium in different organs. However, in the brain, the bacterium was observed only within blood vessels and meninges. In some samples, mild to severe brain tissue damage was seen. In order to understand the virulence and lethality of V. harveyi, a median lethal dose was calculated, and the result was 106 colony-forming units fish-1. To the best of our knowledge, this is the first report that describes V. harveyi isolated from the brain of M. cephalus and validates it as an etiological agent causing neurological signs in this fish species.

Producing flat-head grey mullet Mugil cephalus (Linnaeus, 1758) fries in captivity from sexually mature adults collected in Sardinian lagoons

Mugil cephalus has been identified as a suitable species for feeding populations in developing countries, and it represents a traditionally harvested and consumed species in various European countries. A decline in wild populations and a growing demand have promoted new interest in mullet production in hatcheries, considered imperative for the production of a steady supply of fry and the expansion of M. cephalus aquaculture. In the present study, wild adults collected in Sardinian lagoons were induced to spawn during their natural reproductive period by treating them with a single dose of a slow release GnRHa preparation (200µgkgbw-1). In 2016, a protocol for reducing stress in capturing, transporting and selecting wild adults was set up, and 64% of the females with an oocyte diameter larger than 550µm were successfully induced to spawn. Five spawning induction trials were carried out in the period 2016–2019. The mean fertilization rate and the mean hatching rate obtained were 83±14% and 76±13%, respectively. The individuals obtained were reared indoor in a recirculating aquaculture system (RAS) at a density of 40 individuals L-1 for 60 days, and their survival ranged from 10±2 to 19±1%. During the whole larval rearing phase, from 0 to 34 days post hatching (dph), the mean standard growth rates recorded were 5.0±0.7% in total length and 14.4±3.9% in body weight. The rearing density used resulted in an average survival rate comparable or even better than those obtained by other authors, thus indicating the possibility of producing M. cephalus fries in captivity from sexually mature adults captured in Sardinian lagoons, reducing the costs and optimizing the production.

Morphological and molecular characterization of Neoechinorhynchus (N.) cephali n. sp. (Acanthocephala: Neoechinorhynchidae) Stiles and Hassall 1905 infecting the flathead grey mullet Mugil cephalus (Linnaeus, 1758) from the southwest coast of India

The present paper describes Neoechinorhynchus (Neoechinorhynchus) cephali n. sp., an acanthocephalan parasite infecting the intestine of the flathead grey mullet Mugil cephalus from the southwest coast of India. The parasite exhibited a prevalence of 7.40%, mean intensity of 18.5 and abundance of 18-19 worms/infected host. Morphologically, N. (N.) cephali n. sp. is sexually dimorphic, small, cylindrical, slightly curved and creamy white in colour. Females are larger than males, measured 8.87 × 0.88 mm and 5.65 × 0.66 mm, respectively. Proboscis is armed with three circles of six hooks each, which progressively decreases in size posteriorly. Hooks are backwardly curved and robust and tapering with a sharp, pointed tip, striations on the surface and a manubrium at its base. The body is aspinose, trunk surface with micropores and pits and proboscis surface with papilliform structures. The body wall is with five dorsal and two ventral hypodermal nuclei, along with lacunar canals connected by circular anastomoses. Lemnisci are subequal, small lemnisci are uninucleated, and large ones are binucleated. The cement gland is oval, with four giant nuclei; bursa is with many sensory cells. Eggs are elliptical, with concentric shells, and polar prolongation is absent. In the molecular and phylogenetic analyses based on the 18S ribosomal DNA region, the present species stands out with a high bootstrap value and is positioned as a sister branch of N. (N.) dimorphospinus. Based on the differences in morphology, morphometry and molecular and phylogenetic analyses, the present species of acanthocephalan infecting M. cephalus is considered as new, and the name Neoechinorhynchus (Neoechinorhynchus) cephali n. sp. is proposed.

Integrated multi-trophic aquaculture systems: energy transfers and food web organization in coastal earthen ponds

Three Ecopath models were built to reproduce 3 experimental treatments carried out in earthen ponds located in Olhão, southern Portugal, to understand the energy transferred and the ecosystem state in integrated multi-trophic aquaculture (IMTA). These earthen ponds behave as simplified ecosystems or mesocosms, with well-defined borders, where the relationships between trophic groups can be described through ecosystem modeling. Different combinations of species were produced in these ponds, corresponding to the 3 treatments: (1) fish, oysters and macroalgae (FOM); (2) fish and oysters (FO); and (3) fish and macroalgae (FM). The managed species were meagre Argyrosomus regius, white seabream Diplodus sargus, flathead grey mullet Mugil cephalus, Japanese oyster Crassostrea gigas and sea lettuce Ulva spp. The results showed that the total amount of energy throughput was 15 to 17 times higher when compared with an equivalent naturalized system. The high biomass and low recycling indicated an immature system with low resilience and low stability that demands high rates of water renewal and aeration to maintain good water-quality levels for finfish production. The addition of oysters and macroalgae in the FOM treatment appeared to improve the water quality, since oysters controlled the excess of phytoplankton produced in the ponds by ingesting a fair amount of the phytoplankton, while the macroalgae helped in the absorption of excess nutrients and created a habitat for periphyton and associated macroinvertebrates. Some ecosystem attributes of the FOM ponds approached the values of the naturalized model, suggesting a possible path towards more sustainable aquaculture.

Influence of the Technological Process on the Biochemical Composition of Fresh Roe and Bottarga from Liza ramada and Mugil cephalus.

Bottarga is a high-priced delicacy with high nutritional value, and, in Italy, bottarga from mullets has been recognized to be a traditional food product. The flathead grey mullet Mugil cephalus and the thinlip grey mullet Liza ramada are the main cultured grey mullets in the Mediterranean Sea. In this study, fresh roe and bottarga from these two species were investigated to evaluate the influence of the technological process and the species on their biochemical composition and health advantages. The 1 h/200 g salting-out step did not increase the levels of NaCl in the bottarga, although it highly decreased the levels of some heavy metals like Cu and Al. Processing of fresh roe in bottarga led to an essential modification of the lipid fraction, following a general series of monousatturated fatty acid (MUFA)> poliunsutturated fatti acid (PUFA) > saturated fatty acid (SAFA) and an increase in both ω3 and ω6 in Liza ramada. Moreover, bottarga showed higher levels of squalene and cholesterol and an increased Essential Amino Acid/Total Amino Acid ratio (EAA/TAA) in both species. In addition to the nutritional benefits for the consumer, the process proposed in this study may represent a reliable tool for local producers to obtain a final bottarga with both a reproducible biochemical composition and organoleptic characteristics.

Involvement of sphaeractinomyxon in the life cycle of mugiliform-infecting Myxobolus (Cnidaria, Myxosporea) reveals high functionality of actinospore morphotype in promoting transmission.

Four new actinospore types belonging to the sphaeractinomyxon collective group (Cnidaria, Myxosporea) are described from the coelomic cavity of a marine Baltidrilus sp. (Oligochaeta, Naididae) inhabiting a northern Portuguese estuary. Host identification supports the usage of marine oligochaetes, namely of the family Naididae Ehrenberg, 1828, as definitive hosts for myxosporeans inhabiting estuarine/marine environments. The absence of mixed infections in the host specimens analysed is suggested to reflect the influence of host-, parasite- and environmental-related factors regulating myxosporean-annelid interactions. Molecular analyses matched the SSU rDNA sequences of three of the four new types with those of mugiliform-infecting Myxobolus spp., namely Myxobolus mugiliensis and a Myxobolus sp. from flathead grey mullet Mugil cephalus, and Myxobolus labrosus from thicklip grey mullet Chelon labrosus. These results directly link, for the first time, the sphaeractinomyxon collective group to a myxospore counterpart, further confirming their previously hypothesized specific involvement in the life cycle of myxobolids that infect mullets. Acknowledging this life cycle relationship, the functionality of the sphaeractinomyxon morphotype is suggested to have been decisive for the evolutionary hyperdiversification of the genus Myxobolus in mullets. Unlike other actinospore morphotypes, sphaeractinomyxon lack valvular processes, which implies a limited capability for buoyancy. Considering the benthic-feeding nature of mullets, this feature is most likely crucial in promoting successful transmission to the vertebrate host.

The osteology of the golden grey mullet Liza aurata (Teleostei: Mugiliformes: Mugilidae) including interactive three-dimensional reconstructions.

Grey mullets are remarkably characterized by their overall uniform external morphology. Identifying species as well as positioning the Mugiliformes in a phylogenetic context is rather difficult. Most recently they were placed in the newly erected Ovalentaria, but more detailed relationships to potential sister taxa were not resolved. Studying the internal morphology, especially the osteology, might provide new insights into the evolution of the Mugiliformes as well as help clarify their phylogenetic position within the Ovalentaria. A detailed osteology of the golden grey mullet Liza aurata is presented. The use of cleared and stained specimens allowed for a complete examination of bony and cartilaginous structures, and a 3D reconstruction from a μCT data set provided additional information on the positional relationships of the bones. Following this, the data obtained were compared with different mugilid species, particularly with the flathead grey mullet Mugil cephalus. Several differences between these species could be identified, such as the position of the basisphenoid, the shape of the hyomandibular and the composition of the branchial arches. These characters might help in understanding the evolutionary changes happening within the mugiliforms and will provide the basis to study this taxon in detail, finally allowing the reconstruction of the body plan of grey mullets.

Myxozoan biodiversity in mullets (Teleostei, Mugilidae) unravels hyperdiversification of Myxobolus (Cnidaria, Myxosporea).

Mullets are ecologic and commercially important fish species. Their ubiquitous nature allows them to play critical roles in freshwater and marine ecosystems but makes them more vulnerable to diseases and parasitic infection. In this study, a myxozoan survey was performed on three species of mullet captured from a northern Portuguese river. The results disclose a high biodiversity, specifically due to the hyperdiversification of Myxobolus. Thirteen new species of this genus are described based on microscopic and molecular procedures: 7 from the thinlip grey mullet Chelon ramada, 2 from the thicklip grey mullet Chelon labrosus, and 4 from the flathead grey mullet Mugil cephalus. Myxobolus exiguus and Ellipsomyxa mugilis are further registered from their type host C. ramada, as well as six more myxospore morphotypes that possibly represent distinct Myxobolus species. Overall, the results obtained clearly show that the number of host-, site- and tissue-specific Myxobolus spp. is much higher than what would be expected in accordance to available literature. This higher biodiversity is therefore discussed as either being the result of the usage of poor discriminative criteria in previous studies, or as being a direct consequence of the biological and ecological traits of the parasite and of its vertebrate and invertebrate host communities. Bayesian inference, maximum likelihood and maximum parsimony analyses position the new species within a clade comprising all other Myxobolus spp. that infect mugiliform hosts, thus suggesting that this parasitic group has a monophyletic origin. Clustering of species in relation to the host genus is also revealed and strengthens the contention that the evolutionary history of mugiliform-infecting Myxobolus reflects that of its vertebrate hosts. In this view, the hyperdiversification of Myxobolus in mullet hosts is hypothesized to correlate with the processes of speciation that led to the ecological plasticity of mullets.

Sperm cell ultrastructure of the haplosplanchnid Haplosplanchnus caudatus (Platyhelminthes: Digenea) – An intestinal parasite of Mugil cephalus, and its potential phylogenetic application

The ultrastructural characters of mature spermatozoon of the digenean Haplosplanchnus caudatus were described by means of transmission electron microscopy (TEM). Live parasites were collected from the digestive tract of flathead grey mullet Mugil cephalus (Teleostei: Mugilidae) caught off the Gulf of Gabes in La Chebba (Tunisia). The present study provides the first ultrastructural data on a digenean belonging to the superfamily Haplosplanchnoidea. The spermatozoon of H. caudatus is a filiform cell which exhibits: (i) two axonemes with the 9+‘1’pattern of trepaxonematan Platyhelminthes having about the same length, (ii) an external ornamentation of the plasma membrane associated with cortical microtubules and located in the anterior part of the sperm cell, (iii) spine-like bodies, (iv) two mitochondria containing large mitochondrial matrix granules, (v) a nucleus, and (vi) granules of glycogen irregularly distributed. Moreover, the spermatozoon of H. caudatus displays the Quilichini et al.’s cryptogonimid type of posterior extremity. The mitochondrial matrix granules are described for the first time in a digenean sperm cell.

Changes of salinity and species composition of ichthyofauna in the Azov Sea

The impact of salinity changes on the composition of the Azov Sea ichthyofauna is considered. To date, not only the quantitative, but also the qualitative composition of ichthyofauna and commercial catches has changed, the base on which began to dominate by the Black and Caspian Sea sprat Clupeonella cultriventris, European anchovy Engraulis encrasicolus, gobies Gobiidae, as well as the alien species so-iuy mullet Planiliza haematocheila and Prussian carp Carassius gibelio. In the eastern part of the Taganrog Bay, golden grey mullet Chelon aurata, flathead grey mullet Mugil cephalus and Black Sea brill Scophthalmus maeoticus were registered for the first time. The number of aboriginal semi-anadromous species has decreased many times due to the deterioration of environmental and spawning conditions. The recommendations for the rationalization of fisheries under the conditions of salinization of the Azov Sea are presented.

Taxonomic study on crustacean parasites of the flathead grey mullet (Mugil cephalus) and red seabream (Pagrus major) in Hiroshima Bay, Japan

Crustacean fish parasites can be used as bio-indicators of pollution. This study examined the crustacean parasites of flathead grey mullet (Mugil cephalus) and red seabream (Pagrus major) landed at a fishing port in Hiroshima Bay. Specimens were collected from November 2015 to August 2016. Three species of parasitic crustaceans were identified. Caligus sp. (Copepoda: Siphonostomatoida: Caligidae) was collected from the gills of a male flathead grey mullet Mugil cephalus. The genus Caligus is the largest among the parasitic copepods, containing more than 250 species worldwide, and a total of 20 species have been found from marine fishes in Japan. Lernanthropus atrox Heller, 1865 (Copepoda: Siphonostomatoida: Lernaeopodidae) was collected from the gills of a female red seabream Pagrus. Copepods of the genus Lernanthropus are found attached to the gill filaments of marine fishes in the world. This species is known to occur in both Australian and Japanese waters; in Japan, it has been recorded from Tokyo Bay and the Seto Inland Sea. The cymothoid copepod Ceratothoa verrucosa (Schioedte and Meinert, 1883) (Isopoda: Cymothoidae) was found in the buccal cavity of a red seabream Pagrus major. Cymothoid isopods, including Ceratothoa verrucosa, are found in the buccal and gill cavities as well as on the body surface of fish hosts. This species is only known to occur in Japanese waters.

Modelling environment contamination with heavy metals in flathead grey mullet Mugil cephalus and upper sediments from north African coasts of the Mediterranean Sea

Heavy metals are a serious hazard for aquatic ecosystems and human health. They negatively affect aquatic life functioning through accumulation resulting physiological/growth disturbances in aquatic lifeforms. This survey focused on the assessment of heavy metal pollution in the Gulf of Annaba (northeastern Algeria), the largest and most diversified industrial hub in Africa, using a multi-compartment approach (water–sediment–biota). The study aims to characterize the spatiotemporal variation of trace metal (TM) contamination and its effects on the growth of the Flathead grey mullet (Mugil cephalus). It reviewed TM concentrations in upper sediments and organs of M. cephalus from various hydrosystems worldwide. Five sites distributed along the Gulf were sampled to determine water physicochemical parameters as well as the contamination of surficial sediments and muscles of M. cephalus by zinc, copper, lead, cadmium and mercury. The spatiotemporal variations of the measured parameters were tested and discussed following the synergetic effects of water, sediment and muscle variables on fish biometrics. The sediments at the Port, Joinoville and Sidi-Salem sites were classified as heavily polluted by lead, copper, zinc and cadmium, whereas only at the Port by mercury. Muscular lead concentrations exceeded international standard values in Joinoville and Port, and zinc in Port. The increase of water dissolved oxygen induced a significant decrease in sediment TM. The increase of sediment TM caused a significant increase in muscle TM levels. The S-shaped logistic models indicated that muscle contaminations reached a saturation plateaus following the current sediment pollution. TM concentrations in fish muscles negatively affected fish weight, but only copper and cadmium significantly influenced fish length. The consumption of fish from the Port, Joinoville and Sidi-Salem can be dangerous because concentrations of lead, zinc and cadmium exceeded the international standards. This study validates the effectiveness of biomonitoring using M. cephalus as bioindicator in polluted coasts.

Comparative study of haematology of two teleost fish (Mugil cephalus and Carassius auratus) from different environments and feeding habits

Haematological parameters are valuable indicators of fish health status. This study is aimed to provide baseline data of the blood profile of two teleost fish species living in different environments and with divergent feeding behaviour, namely the flathead grey mullet Mugil cephalus Linnaeus, 1758, a marine herbivorous fish, and the goldfish Carassius auratus (Linnaeus, 1758), a freshwater omnivorous fish. Using an automated system coupled with flow cytometry and light microscopy, significant variations were found between M. cephalus and C. auratus blood parameters, except for haemoglobin concentration (Hgb). A significant increase in red blood cell count (RBC) and haematocrit (Hct) levels, associated with reduced mean corpuscular volume (MCV), was revealed in mullets in respect to goldfish. These data may be attributable to differences in fish species, or to their divergent physiological activeness as high RBC values are associated with fast movement and high activity with streamlined bodies, or to environmental factors such as water salinity, an increase in which may lead to erythropoiesis as an adaptive process in seawater fish. Additionally, lower values of white blood cell count (WBC) and thrombocyte count (TC) were recorded in mullets with respect to goldfish, and these changes may be due to divergent feeding habits of the two fish species, or to their different environments since increased salinity may inversely affect WBC. Overall, findings from this study provide a better understanding of the influences of divergent environmental conditions and feeding habits on fish blood parameters. The combined use of an automatic haematological count with flow cytometry was demonstrated to be effective for an early assessment of blood parameters in different fish species.

Some aspects of the reproductive physiology of the Flathead grey mullet Mugil cephalus (Linnaeus, 1758) in Benghazi coast, eastern Libya.

The reproductive physiology of 530 specimens of Mugil cephalus (Family: Mugilidae) were collected from catches by gill and trammel nets operating on Benghazi coast on Mediterranean Sea - Libya was studied, there were monthly variations in sex ratio and a tendency for females (298 fish = 56.2%) than males (232 fish = 43.8%) for the whole population, Overall sex ratio was (1 : 1.28) for males to females respectively, First maturation size was determined for females L50 = 34.1 cm and for males L50 = 32.3 cm, All individuals have definite breeding season which extends from July to October, An increase in Oocyte diameters was evident in July (489 µ ± 5.34), and this increase continued in the following months till October (599 µ ± 11.04), the absolute fecundity ranged from 578981 to 2598022 for fish total length ranging from 19.5 to 47.4 cm, whereas relative fecundity ranged from 29036 to 57352 / cm.

The effect of acute hypoxia on swimming stamina at optimal swimming speed in flathead grey mullet Mugil cephalus

Flathead grey mullets Mugil cephalus are commonly found in Mediterranean lagoons, which are regularly subject to high environmental variations. Oxygen is one of the factors that shows extremely high variation. The objective of this study was to test the effects of acute hypoxia exposure at two experimental temperatures (i.e. 20 and 30°C) on the stamina (time to fatigue) in M. cephalus swimming at the minimal cost of transport (i.e. optimal swimming speed; Uopt). At each temperature, a relationship was established between swimming speed and oxygen consumption (MO2). This allowed estimation of Uopt at 45 cm s−1 (~1.12 Body Length s−1). Independent of temperature, stamina at Uopt was significantly reduced in severe hypoxia, i.e. at 15% of air saturation (AS). In these conditions, oxygen supply appears therefore to be insufficient to maintain swimming, even at the low speed tested here. After the stamina test, MO2 measured in fish tested at 15% AS was significantly higher than that measured after the test in normoxia. Therefore, we suggest that in hypoxia, fish used anaerobic metabolism to supplement swimming at Uopt, leading to an oxygen debt. Since flathead grey mullet is a hypoxia-tolerant species, it is possible that hypoxic conditions less severe than those tested here may reduce stamina at low speed in less tolerant species. In addition, we suggest that testing stamina at these speeds may be relevant in order to understand the effect of hypoxia on behavioural activities carried out at low speed, such as food searching.